Equilibrium and kinetic study on
chromium
(VI) removal from simulated
waste water using gooseberry seeds as a novel biosorbent
*J. Aravind; G. Sudha; P. Kanmani; A.J. Devisri; S. Dhivyalakshmi; M. Raghavprasad
Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India
A B S TR AC T: Gooseberry seed (Phyllanthus acidus) was used as an adsorbent to determine its feasibility for the removal of chromium (VI). Various parameters such as pH, temperature, contact time, initial metal concentration and adsorbent dosage were investigated to determine the biosorption performance. Equilibrium was attained within 60 minutes and maximum removal of 96% was achieved under the optimum conditions at pH 2. The adsorption phenomenon demonstrated here was monolayer represented by Langmuir isotherm with R2 value of 0.992 and the Langmuir constants k and q0 was found to be 0.0061 (L/mg) and 19.23 (mg/g). The adsorption system obeyed Pseudo second order kinetics with R2 value of 0.999. The results of the present study indicated that gooseberry seed powder can be employed as adsorbent for the effective removal of hexavalent chromium economically.
Keywords: Biosorption, Cr(VI), Equilibrium, Gooseberry seed, Isotherm, Kinetics, Removal ISSN 2383 - 3572
*Corresponding Author Email:[email protected] Tel.: +91 422 266 9401; Fax: +91 422 266 9401 Note. This manuscript was submitted on February 12, 2015; approved on April 17, 2015; published online on June 1, 2015. Discussion period open until October 1, 2015; discussion can
be performed online on the Website “Show article” section
for this article. This paper is part of the Global Journal of Environmental Science and Management (GJESM).
Received 12 February 2015; revised 12 April 2015; accepted 17 April 2015; available online 1 June 2015
INTRODUCTION
Rapid industrialization and urbanization have resulted in exponential discharge of industrial effluents and toxic heavy metals in to aquatic and terrestrial ecosystem (Das et al., 2007; 2013). Chromium metal, which is currently explored in this research work, is present mainly in leather tanning, precious metal mining and electroplating industrial effluents, according to US EPA, Chromium is considered to be the topmost priority toxic pollutant. Chromium metal in its natural form is found to exist in two states: Cr(III) and Cr(VI). Hexavalent chromium is 100 times more toxic than trivalent chromium and due to its toxicological and carcinogenic consequences, it is likely to cause detrimental health hazards (Rao and Parbhakaret al.,2011). According to AWWA permissible level of Cr(VI) ion in surface
and portable water are 0.1 and 0.05mg/L respectively (APHA, 2005). Thus, it becomes top priority to make effluents free from Cr(VI) before releasing into the environment.
Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015J. Aravind et al. suggested as suitable biosorbent for heavy metal
sequestration (Nguyenet al., 2013). Currently locally available agricultural waste residues are an automatic choice for remediation of heavy metals, they are also being considered as an important source of biosorbents due to the presence of certain functional groups such as hydroxyl, ester, amino, carboxyl, carbonyl, sulphydryl, and phosphor group to which heavy metal bind. In this context, Gooseberry seed powder (Phyllanthus acidus), a novel biosorbent was examined for Cr(VI) binding efficiency. In the present study, various parameters which influence Cr(VI) removal such as pH, initial metal ion concentration, contact time and adsorbent dosage were investigated in a batch mode. Analytical techniques such as FTIR and SEM were employed for biosorbent characterization. FTIR analysis was employed to determine the active site responsible for biosorption based on the changes in vibrational frequencies of the functional groups. The surface morphology and the porosity of the biosorbent were investigated by SEM analysis. Investigations on equilibrium isotherm and adsorption kinetics were also carried out to understand the adsorption mechanism. The present work was carried out at Coimbatore during the period of December 2014 to February 2015.
MATERIALS AND METHODS
Biosorbent material
Gooseberry seeds were procured locally (Coimbatore, India). The seeds were washed under running tap water and were subjected to drying in hot air oven at an optimum temperature of 40°C. Then the seeds were ground and sieved. The finely powdered biosorbent was subjected to washing. After washing with distilled water, the mixture was filtered and dried at 50°C for a period of 1 h. The dried powder was stored in an air tight container to prevent moisture. The dried powder was used as a biosorbent for the experiment.
Batch studies
The maximal adsorption efficiency of biosorbent was determined by varying several parameters which influence the adsorption phenomenon, such as pH, contact time, adsorbent dosage and initial metal concentration by fixing the volume of metal solution to 100ml. After agitating for 30 min in a temperature controlled orbital shaker at 120rpm, the solution was centrifuged. The residual concentration
of chromium present in the supernatant was determined spectrophotometrically using 1, 5 Diphenyl carbazide reagent as a complexing agent at 540 nm (APHA method 3500-Cr).
Chromium removal analysis
Chromium removal was estimated using 1,5 Diphenyl carbazide as a complexing agent spectro-photometrically. Different standards containing less than 100 mg/L (20, 40, 60, 80, and 100) were prepared and maintained at pH less than 2. To 10 ml of standard, 0.2 ml of diphenyl carbazide was added as a complexing agent. The solution was incubated until red violet color was developed. The absorbance was noted at 540 nm using visible spectrometer (Systronics-106). A blank was prepared for Cr (VI) analysis. The amount of chromium present in the sample was determined from calibrated curve according to the standard method (APHA method 3500- Cr).
Removal efficiency
The percentage of Chromium removal (R %) was determined using the below equation:
Removal efficiency (R %) = (1)
Ci and Co represents the initial and final concentration of chromium metal in mg/L.
Adsorption isotherm
Adsorption isotherm aids in the evaluation of adsorption efficiency of any adsorbent and also faci litate in quantifying the corr elatio n of equilibrium with the amount of adsorbate present in the solution and relate the quantum of adsorbate adsorbed in to any bioresource material at a given temperature.
Adsorption capacity is given by the empirical relation:
qe
Where qeis the adsorption capacity (mg/g), Ci and C0 are initial and final metal concentration (mg/L), m is the mass of the adsorbent (g) and V is the volume of the metal solution (L). In the present study, adsorption of Cr(VI) with the help of gooseberry seed powder was investigated by employing various adsorption isotherms.
Ci 100
(Ci - C0)
m V
Langmuir adsorption isotherm
This model is based on the assumption that metal uptake takes place on the homogeneous surface by monolayer adsorption. It involves uniform energies of adsorption. Langmuir adsorption isotherm is represented by the empirical equation:
Where q is the amount of solute adsorbed per amount of adsorbent (mg/g), K (L/mg) and q0 (mg/g) are the Langmuir constants related to energy of adsorption and maximum monolayer capacity and y is the solute concentration in the solution (mg/L). By plotting 1/q versus 1/y, Langmuir parameters were obtained (Langmuir, 1917).
Freundlich adsorption isotherm
Freundlich adsorption isotherm is theorized, that metal uptake takes place on the heterogeneous surface of an adsorbent by multilayer adsorption. It involves non uniform energies of adsorption. Freundlich adsorption isotherm is given by the empirical equation:
Where qe is the amount of solute adsorbed per amount of adsorbent (mg/g), y is the solute concentration in the solution (mg/L), K and n are the Freundlich constants related to adsorption capacity and intensity. By plotting lnqe versus lny, Freundlich constants k and n were obtained. It also determines the heterogeneity of surface pore distribution and the value of n indicates the favorability of adsorption (Freundlich, 1906).
Temkin adsorption isotherm
Temkin model is based on the concept that the heat of adsorption of all molecules decreases linearly with coverage due to adsorbate-adsorbent interaction. It involves uniform distribution of binding energies up-to some maximum binding energy.
Temkin adsorption isotherm model is represented by the linearized form of equation:
Where, BT= (RT)/bT,T is the absolute temperature in Kelvin and R is the universal gas constant. The constant bTis related to heat of adsorption (J/mol), AT is the equilibrium binding constant (1/L/min). By plotting qe versus lnY, Temkin constants such as BT and AT were determined (Temkin and Pyzhev, 1940).
Adsorption kinetics
Studies on adsorption kinetics had been carried out to describe adsorption mechanism and diffusion process. The generated data were tested using Pseudo first order and second order kinetics equation.
Pseudo first order / lagergren kinetic model
This model was derived based on adsorption capacity. The overall adsorption rate is directly proportional to the driving force i.e., the difference between the initial and equilibrium metal concentration (Qiuet al.,2009). The equation can be represented as follows:
Where qe is the amount of solute adsorbed at equilibrium per unit mass (mg/g), qt is the amount of solute adsorbed at any time t (mg/g), K1 is the pseudo first order rate constant (1/min). Integrating the above equation under boundary conditions yields the following equation:
Pseudo second order kinetic model
According to this model, the driving force (qe-qt) is proportional to the available fraction of active site. The equation can be expressed as follows:
Integrating under boundary conditions such as q=0 to q>0 and t=0 to t>0 and further simplification yields the following equation:
Where Vo= k2qe2, V
o is the initial adsorption rate (mg/ gmin) and k2 is the pseudo second order rate constant (g/ mg/min). Adsorption parameters such as V0, qe, k2 can be determined by plotting t/qt versus t (Ho and McKay, 1999).
(3)
ln qe = lnk + lny1n (4)
qe = BTlnAT + BTlnY (5)
1 q0 k q0y + = 1 q
(6) = K1 (qe - qt)
dqe dt
(7) log (qe - qt) = log qe - tK1
2.303
= K2 (qe - qt)2 dq
dt (8)
(9) 1
qe 1 V0 t
Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015Chromium removal using gooseberry seed powder
RESULTS AND DISCUSSION
FT-IR analysis
To understand the capability of gooseberry seeds as an efficient adsorbent for chromium removal, FT-IR analysis was carried out to determine the functional groups present in the adsorbent based on the changes in the vibrational frequencies. The functional groups representing each peaks and stretch are given in the Table 1. The shift in the peak from 3317.57 to 3417.66 1/cm indicated that stretching of -OH group was responsible for the binding of Cr(VI) ions onto the adsorbent. It was found that C=O, C-H, C-N stretch, N-H and C-H bend were also responsible for the effective removal of Cr(VI) ions as it can be elucidated from Fig. 1. Similar results were obtained by Muthukumaran and Beulah, (2010), where stretching of O-H group was responsible for the adsorption of
Cr(VI) using chemically activated S yzyg iu m jambolanum nut carbon.
SEM analysis of Gooseberry seed powder
Metal adsorption capacity of any biosorbent material can be comprehended by surface morphology analysis using SEM, where presence of many pores indicates the possibility of higher metal sorption. The Surface morphology of gooseberry seed powder (GSP) was found to be highly porous with different shape and size (Fig. 2). The SEM micrograph taken after sorption showed irregularities and decrease in pore size. The formation of white layer on the surface of the sorbent indicates that the sorbent is loaded with Cr(VI) ions (Aravindet al., 2013).
Table 1: FT-IR spectral characteristics of gooseberry seed powder before and after adsorption IR Peak
1 2 3 4 5 6
Before adsorption (1/cm) 3317.57 2862.36 1728.22 1527.62 1049.28 609.51
After adsorption (1/cm) 3417.66 2854.65 1720.50 1519.91 1058.99 617.22
Studies on effect of pH
pH is the most important parameter in heavy metal biosorption. At aqueous phase, Cr(VI) exist in several anionic forms such as chromate CrO42- (pH>6), dichromate Cr2O72- and HCrO4- (pH:1-6). It is observed from Fig. 3 that the removal percentage decreases with an increase in pH from 2 to 7. Maximum removal was obtained at pH 2 indicating the influence of pH in
protonation and deprotonation of adsorbent. As the pH is lowered, the surface of the adsorbent becomes protonated and most of the chromium exists as anionic species. Therefore large number of protons in the adsorbent could easily coordinate with the metal ions present in the solution through electrostatic interaction, whereas the removal percentage sharply decreases with an increase in pH from 2 to7 due to the deprotonation Fig. 2: SEM images of gooseberry seed powder (GSP) before and after chromium adsorption
0 10 20 30 40 50 60 70 80 90 100
0 1 2 3 4 5 6 7 8
Fig. 3: Effect of pH with 100 mg/L metal concentration, adsorbent dosage of 0.1g/100 ml, contact time of 30 min and speed of 120 rpm
(A) SEM micrograph before adsorption (B) SEM micrograph after adsorption
Effect of pH
p H
Re
m
ov
al
(%
Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015J. Aravind et al.
of adsorbent. The adsorbent surface becomes negatively charged and there exists electrostatic repulsion between anionic form of chromium and adsorbent. Similar results were obtained with Eucalyptus bark (Sarin and Pant, 2006).
Effect of adsorbent dosage
Adsorbent dosage plays a major role in adsorption process. From the result, as shown in the Fig. 4, it is understood that, with an increase in adsorbent dosage from 0.1 to 0.5 g, there exists an increase in percentage removal from 51 to 92% and the maximum removal was attained at the adsorbent dosage of 0.5 g. The observed trend may be due to greater availability of surface area and functional groups at higher adsorbent dosage (Suresh and Babu, 2008). As a result, electrostatic interaction occurs between the functional groups present in the active site of the adsorbent and the metal ions present in the solution, similar trends were reported by Deviet al.,(2012).
Effect of contact time
Percentage removal of Cr(VI) ions was measured as a function of time to establish an appropriate contact time between adsorbent and adsorbate. Fig. 5 indicates that the percentage removal of Cr(VI)
0 10 20 30 40 50 60 70 80 90 100
0 0.1 0.2 0.3 0.4 0.5 0.6
Fig. 4: Effect of adsorbent dosage with metal concentration of 100 mg/L with contact time of 30 min and speed of 120 rpm at pH 2
ions from the solution is higher at the beginning due to greater availability of surface area and functional groups. With an increase in time, it was found that there exists a control in metal uptake rate, since the functional groups present in the surface of the sorbent gets exhausted. It was found that maximum removal was obtained within 30 minutes and equilibrium was attained within 60 minutes. The results obtained were in agreement with Talokar, (2011) where maximum removal was described at a contact time of 30 minutes. Thus equilibrium time of 60 minutes was selected for further studies.
Effect of initial metal concentration
The experiments were performed by varying the initial metal concentration from 20 to 100 mg/L, while the contact time was varied from 15 to 60 minutes at a constant adsorbent dosage of 0.5 g/100 ml at pH 2 and an agitation speed of 120 rpm. Cr(VI) removal as a function of contact time and initial metal concentration is given in the Fig. 6. From the Fig. 6, it is clear that with an increase in metal concentration from 20 to 100 mg/L, removal percentage decreases from 97 to 88 with an increase in adsorption capacity. The maximum removal was obtained within 15 minutes, after which there was Effect of adsorbent dosage
Re
m
ov
al
(%
)
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70
R em ov al (% )
Time (min)
Effect of contact time
Fig. 5: Effect of contact time with 100mg/L metal concentration, 0.5g/100ml adsorbent dosage, and speed of 120 rpm at pH 2
0 10 20 30 40 50 60 70 80 90 100
0 10 20 30 40 50 60 70
R (% )
Time (min)
Effect of Initial metal concentration
20 (mg/L) 40 (mg/L) 60 (mg/L) 80 (mg/L) 100 (mg/L)
Fig. 6: Effect of initial metal concentration with adsorbent dosage of 0.5g/100ml and speed of 120rpm at pH 2
negligible removal since the surface of the sorbent gets exhausted after the formation of one layer thickness of metal ions and then metal uptake rate is
controlled due to the transport of ions from exterior to interior site of the adsorbent.Similar trend was observed with ternary biopolymeric microspheres Effect of contact time
Re
m
ov
al
(%
)
Time (min)
Time (min)
R
(%
)
Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015Chromium removal using gooseberry seed powder
y = 0.117x + 0.051 R² = 0.992
0 0.05 0.1 0.15 0.2 0.25
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
1/
qe
1/y
Langmuir isotherm
A
y = 0.4937x + 1.7416 R² = 0.9907
1.4 1.9 2.4 2.9 3.4
-0.5 0 0.5 1 1.5 2 2.5 3
ln
qe
ln Y Freundlich isotherm
B
y = 4.484x + 5.847 R² = 0.990
0 2 4 6 8 10 12 14 16
-0.5 0 0.5 1 1.5 2 2.5
qe
ln Ce
Temkin isotherm
C
Fig. 7: (A; B; C): Equilibrium isotherms for Cr(VI) removal on gooseberry seed powder (pH 2, temperature 37°C, metal concentration 100 mg/L)
1/
qe
ln
qe
Langmuir isotherm
1/y
Freundlich isotherm
ln Y
Temkin isotherm
qe
ln Ce
A
B
(Bajpai and Rai, 2010). The data generated due to effect of initial metal concentration helps in determining the equilibrium concentration(Ce), adsorption capacity(qe), metal uptake rate and kinetic characteristics.
Equilibrium isotherms
Isotherms have been used to describe the equilibrium relationship between the amount of solute that is present in the solution and adsorbent (Aravind et al., 2013). In the present study, Langmuir, Freundlich and Temkin models were employed. The best equilibrium model was determined based on correlation coefficient. Fig. 7.A-7.C represents the investigations over various adsorption isotherms on Cr(VI) removal. Under the optimal conditions, the metal adsorption equilibrium was very well represented by Langmuir isotherm which accounts for existence of monolayer adsorption on homogeneous surface. Langmuir constants q0 and k evaluated from the slope and intercept are 19.23 (mg/g) and 0.0061 (L/ mg) respectively with the correlation coefficient of 0.992. Higher R2 value indicates the strong binding of Cr(VI) ions to the adsorbent. Gooseberry seed powder was found to have better adsorption capacity which indicates the favorability of Langmuir isotherm as shown in the Fig. 7.A. The
slope and the intercepts evaluated from the Figs. 7A, B, C are given in Table 2.
Adsorption kinetics
Studies on adsorption kinetics were carried out in order to determine the metal uptake rate. The effect of initial metal concentration was investigated to determine the best kinetic model. Pseudo first order kinetics model were applied by plotting log (qe-qt) versus time as shown in the Fig. 8.A. The obtained R2 value was found to be 0.994 and the results obtained were found to be in agreement with the results obtained from the biosorption of Cr(VI) using the husk of Bengal gram (Ahalyaet al., 2005). Pseudo second order kinetics model were applied by plotting t/qt versus time. From the Fig. 8. B,R2 Value was observed to be high (0.999) which implies adsorption mechanism obeys Pseudo Second order. Various constants determined from kinetics study are given in the Table 3. The results obtained were similar when granular activated carbon was used as an adsorbent (Gholipouret al., 2011).
Comparison of gooseberry seeds as an adsorbent In the present study the performance of gooseberry seeds as an effective and economical adsorbent material with other adsorbent available in
Table 3: Constants evaluated from kinetics study
Table 2: Constants evaluated from various isotherms Isotherms
Freundlich
Langmuir
Temkin
Parameters K value n value K value qovalue
AT Value
BT Value
5.47(mg/g(L/mg)1/n)
2.482 0.0061(L/mg) 19.23(mg/g) 5.9(L/mg) 5.118(J/mol)
R2value
0.990
0.992
0.990
Kinetics Pseudo first order
Pseudo second order
Parameters K1 Value
qe Value
K2Value
qe Value
0.0483 18.57 0.0184 20.83
R2
0.994
Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015J. Aravind et al.
y = -0.0214x + 0.6295 R² = 0.994
-0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4
0 10 20 30 40 50
lo g( q e-qt )
Time (min) Pseudo first order kinetics
A
y = 0.0483x + 0.1253 R² = 0.9997
0 0.5 1 1.5 2 2.5 3 3.5
0 10 20 30 40 50 60 70
t/qt
Time (min) Pseudo Second order kinetics
B
Fig. 8: (A; B): Adsorption kinetics of Cr(VI) removal on gooseberry seed powder at metal concentration of 100 mg/L at 37°C
Pseudo first order kinetics
lo
g(q
e-qt
)
Time (min)
Time (min) Pseudo Second order kinetics
t/
qt
Table 4: Comparison of gooseberry seeds on chromium adsorbent
Adsorbent Adsorption Capacity (mg/g) References
Waste tea 1.55 Orhanet al.,(1993)
Formaldehyde modified saw dust 3.60 Baralet al., (2006)
Paper mill sludge 7.40 Calaceet al.,(2002)
Treated saw dust of Indian rosewood 10 Karthikeyanet al.,(2005)
Coconut shell carbon 10.88 Karthikeyanet al.,(2005)
Tamarind seeds 11.08 Sureshet al.,(2006)
Sugarcane bagasse 13.4 Karthikeyanet al.,(2005)
Rice bran 12.34 Singhaet al.,(2011)
Rice straw 12.17 Singhaet al.,(2011)
Hyacinth roots 15.28 Singhaet al.,(2011)
Rice husk 11.39 Singhaet al.,(2011)
Neem bark 19.60 Singhaet al.,(2011)
Neem leaves 15.95 Singhaet al.,(2011)
Coconut shell 18.69 Singhaet al.,(2011)
Beech saw dust 16.1 Karthikeyanet al.,(2005)
Hazelnut shell activated carbon 17.70 Ciminoet al.,(2000)
literature, on its ability to remove the chromium metal from the synthetic effluent. The gooseberry seeds were found to be effective and better than many adsorbent used for chromium removal (Table 4).
CONCLUSION
The gooseberry seed powder was found to be a better adsorbent based on its efficiency in the removal of chromium, with 96% efficiency, under optimum condition like pH of 2, dosage of 0.5g and equilibrium attained within 60 minutes. Langmuir isotherm was found to be the best fit with an adsorption capacity of 19.23 mg/g and the adsorption mechanism observed Pseudo second order kinetics. Hence the gooseberry seed powder can be claimed as good for removal of chromium from industrial effluents.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.
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Global J. Environ. Sci. Manage., 1(3): 233-244, Summer 2015
AUTHOR (S) BIOSKETCHES
Aravind, J.,M.Sc., M.Tech., Ph.D(Tech). Assistant Professor (Sr), Department of Biotechnology, Faculty of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email:[email protected]
Sudha, G.,B.Tech., Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email:
Kanmani, P.,M.E., Ph.D. Assistant Professor (Sr), Faculty of Biotechnology, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email: [email protected]
Devisri, A.J., B.Tech Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email:
Dhivyalakshmi, S.,B.Tech Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email:
Raghavprasad, M.,B.Tech Department of Biotechnology, Kumaraguru College of Technology, Coimbatore 641049, India. Email:
How to cite this article: (Harvard style)
Aravind, J.; Sudha, G.; Kanmani, P.; Devisri, A.J.; Dhivyalakshmi, S.; Raghavprasad, M., (2015). Equilibrium and kinetic study on Cr(VI) removal from simulated waste water using gooseberry seeds as a novel biosorbent, Global J. Environ. Sci. Manage., 1(3): 233-244.
Chromium removal using gooseberry seed powder Talokar, A.Y., (2011). Studies on removal of chromium
from waste water by adsorption using low cost agricultural biomass as adsorbents, Int. J. Adv. Biotechnol. Res., 2(4): 452-456 (5 pages).
